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Intumescent coatings are usually used as fire protection for steel structures in busy public places. This guide, sponsored by Jotun, looks at how intumescent film products react to heat and flame and how they are applied, as well as regulations and certifications

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The exterior of the Selfridges department store in Birmingham-the main structural steel behind the wall and roof structure has been protected with an intumescent coating

The fire protection of the building allows residents time to escape, and emergency service personnel have the opportunity to enter the area to put out the fire. However, research—and recent tragic events—shows that many buildings have incorrect or inadequate fire protection installations.

It is vital that buildings are designed with fire protection systems to help save lives and reduce the risk of structural collapse. All those involved in building design and construction are responsible for improving the quality of fire protection through the use of best practices and best products.

This CPD will study the role of intumescent coatings-these coatings are specially formulated to react chemically when heated, thereby changing their physical properties, thereby providing fire protection through insulation and cooling effects.

Modern design increasingly uses steel as an architectural feature. When using steel structures, intumescent coatings are usually the first choice for fire protection. The film expansion product can be used in places where many people gather, such as airports, offices, stadiums or shopping malls.

When exposed to fire, ordinary building materials lose their strength-concrete cracks and peels; wood burns and turns into charcoal. Fire prevention can inhibit the failure of these building materials within a predetermined period of time. It should be noted that steel will begin to lose its strength at about 400°C. At 550°C, nearly two-thirds (60%) of the steel's load-bearing capacity will fail.

Film intumescent coatings are specially formulated to react chemically when heated to change their physical form, thereby providing fire protection through heat insulation and cooling effects.

When the steel reaches a temperature of around 250°C, the expansion agent will begin to expand. Depending on the selected product and the dry film thickness (DFT) of the application, the steel can be protected for 15 minutes to up to 3 hours.

The DFT of an intumescent coating can expand to 50 times its original thickness, turning it into soft, lightweight charcoal. When fully expanded, the carbon forms an insulating barrier to protect the steel structure.

Uncoated steel requires 5 to 15 minutes to reach the critical core temperature. Steel begins to lose strength when heated to 400°C and fails at 550°C.

When specifying paint systems (primers and topcoats) to be used in combination with intumescent coatings, it is important to specify approved primers and topcoats. If the wrong primer or topcoat is used, the expansion agent may not work as expected and may fail prematurely.

A water-based swellable film used in the construction phase. Middle image: Dubai Metro, using expanded materials in the structural steel of the station and the footbridge on the road

Cellulose fires are triggered by combustible materials such as wood, paper, furniture, and textiles, and are characterized by a gradual increase in temperature to a peak of 940°C in 10 to 25 minutes. 

Hydrocarbon pool fires are triggered by hydrocarbons (such as oil and natural gas). The flame temperature is high, reaching 1,000°C almost immediately after ignition. After about five minutes, the heat rose to 1,100°C.

In order to evaluate the burning rate, the fire protection industry traditionally uses burning curve data. The cellulose and hydrocarbon combustion curves are the most commonly used temperature curves. The cellulose combustion curve was used for many years in the early 1900s until the hydrocarbon combustion curve was developed in 1970. When the burning rate of plastic, wood, paper, cotton or textiles does not match the burning rate of compounds such as gasoline and chemicals, the latter is much higher.

The standard combustion curve of a cellulose fire reaches 500°C in five minutes, and its development is relatively slow, although its intensity may eventually reach or even exceed the intensity of a hydrocarbon fire.  

Three types of fire protection systems are used in infrastructure buildings: active, passive and reactive. 

These systems are designed to suppress and extinguish flames with water, foam, powder or inert gas. They can effectively reduce the amount of oxygen that can be used as fuel and can act as a coolant. These systems can effectively eliminate fires:

The characteristic of passive fire protection system is that the material does not change its physical form when heated, and it provides fire protection by virtue of its physical or thermal insulation properties. These systems are more commonly used in building areas that require little or no decoration:

These are thin-film intumescent coatings, specially formulated to provide a chemical reaction when heated to change their physical form, thereby providing fire protection through thermal insulation and cooling effects.

Reactive intumescent coatings have a decorative appearance and can be used for steel structures in buildings. The dry film thickness (DFT) range-the thickness of the coating measured on the substrate-can range from 200 microns to 5,000 microns, depending on the fire protection time and the size of the steel to be protected. Epoxy expansion agents have higher film thicknesses of up to 30,000 microns, but the appearance of rough surfaces is not generally used for decorative surfaces.

Expanding materials increase in volume and decrease in density when heated. It is a passive flame retardant and fire retardant, which can protect the steel surface from further thermal erosion. In the event of a fire, some coatings will soften, react and decompose, forming a carbon barrier. The foaming agent generates foam and non-combustible gas, causing the layer to expand significantly to form an effective barrier.

Intumescent DFT will vary according to the fire protection time, steel size, construction use and building complexity, while the approval of intumescent DFT depends on the country, or in some cases will be guided by regional requirements.

A worker applies an intumescent coating on pre-primed steel. Below: An overview of Meydan Racecourse, where the thin-film intumescent coating is designated for its "paint-like" appearance

There are many types of steel profiles, commonly known as universal beams and universal columns, also called I-beams and universal columns. The size and weight of each steel section type may be different, and may have different DFTs according to the fire protection time.

The lighter the size of the steel section, the faster the temperature of the steel section will rise, so the thickness of the film expansion material required is greater. The heavier the steel section size, the slower the steel heats up-so it requires less expansion coating.

The size and temperature limit of the steel section are then used to determine the required fire protection thickness. 

Legislation and regulations determine the requirements for fire protection and performance.

What is important is that there is also a "proof of performance" from a third party who witnessed the test. The certification method provides manufacturers with a method to independently prove the performance of their products, and provides guarantees for the specification makers and purchasers that the certified products will be implemented.

The industry’s rigorous testing procedures simulate the actual conditions of weathering, applied loads, and temperature extremes under typical local environmental conditions.

Regulations and certifications apply not only to finished products applied to structures, but also to the entire process from raw materials to manufacturing to logistics. This ensures that the final product will have the same high-quality, certified expander no matter where it is produced in the world.

Fire protection requirements around the world meet different standards, depending on the country and its building regulations, which presents a unique set of challenges that passive fire protection (PFP) coatings must comply with. 

Dubai Metro-Intumescent paint and topcoat are applied to exposed structural steel to provide fire protection for up to 120 minutes

Intumescent paint must be applied to the newly primed structural steel.

The condition and age of the primer is very important. It must be approved and compatible with intumescent products. The primer is applied to protect the steel substrate from corrosion. It lays a good foundation for the subsequent intumescent paint coating.

A topcoat can be applied to intumescent materials for aesthetic purposes, where steel structures are expressed as architectural features or environments that require durability. It is important to use an approved top coat. 

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